Foliar Fertilization of Soybean Where, When, and Why? Antonio P. Mallarino Iowa State University

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1 Foliar Fertilization of Soybean Where, When, and Why? Antonio P. Mallarino Iowa State University

2 Foliar Fertilization Crops can use foliar-applied nutrients. High salt or ammonia concentrations damage leaf tissue. Known to be useful for application of micronutrients to high-value vegetable and orchards mainly because small amounts are needed. Could supplement primary P, K, S preplant application to soil.

3 Spraying Soybean at Late Growth Stages N-P-K N-P-K-S Nitrogen

4 Nutrition at Reproductive Stages Remediate too low pre-plant fertilization Reduced root activity during late seed development stages. Increased translocation of nutrients and carbohydrates to the seed. Leaf senescence, low photosynthesis. Foliar fertilization could increase and green leaf area duration, protein and carbohydrate synthesis, and grain yield.

5 Iowa Research at Late Stages Dr. Hanway s work in the middle 70's. Sprayed soybean with various nutrient mixtures, frequencies of applications, and at several reproductive stages. Concluded that N-P-K-S increased soybean yield. A ratio (N-P K 2 O-S), close to the ratio in grain, was the best.

6 Spraying NPKS at Late Stages YIELD INCREASE (bu/acre) NPKS RATES 1974, , , , R4 & R5 R5 & R6 R5 & R6.5 R5 & R7

7 Spraying N, NPK, or NPKS But many trials across the Midwest and South from the late 1970's to the middle 1980's did not reproduce the results Example: TVA-Sponsored Research Spray Soybean yield Trials times Check With % loss

8 More Recent Research Mainly research with Nitrogen Minnesota: many fields in the early 2000's, no yield increase or decrease Kansas: in the mid 1990's, yield increase in high-yield conditions under irrigation, response in six of eight fields Nebraska: late 1990's to 2000's, no clear results, mainly no response

9 Spraying Soybeans at Early Growth Stages N-K N-P-K N-P-K-S N-P-K-S-Micros

10 Nutrition at Early Vegetative Stages Low rates of foliar-applied fertilizer can supplement soil fertilization when N fixation or NPKS uptake are limited. Could stimulate plant growth and nutrient uptake during early growth. Could be cost-effective if applied mixed with some post-emergence herbicide. Yield responses were shown in cotton.

11 Iowa Research Projects Mazhar Haq Mark Wuebker Daniel Kaiser J.C. North David Wittry Louis Thompson Daniel Conroy Many Iowa Farmers

12 Foliar Fertilization Projects Chisel-disk, no-till, ridge-till systems. Spray at early growth stages (V5 -V7) 38 trials with NPK mixtures trials with NPK, NPKS, NPKS + micros In 1997 and on-farm trials with , from 1998 to 2002, strips or conventional plot trials Interactions with fungicide application 5 trials with 8 treatments. In 2005 and 2006.

13 Method & Time of Application Rates from 2 to 6 gal/acre, one or two applications. 1st spray at V5, usually 4 to 6 open true leaves across the field. 2nd spray 8 to 10 days later. In strip trials, fertilizer was mixed with Roundup. Measured soil tests, grain yield, growth, and nutrient uptake.

14 First Set of Trials FIELDS 7 RESPONSIVE FIELDS SOYBEAN YIELD (bu/acre) Check 2 gal gal gal gal gal

15 Second Set of Trials FIELDS 6 RESPONSIVE FIELDS SOYBEAN YIELD (bu/acre) Check 2+2 gal gal gal gal gal 8-0-8

16 Third Set of Trials FIELDS 5 RESPONSIVE FIELDS SOYBEAN YIELD (bu/acre) Check 3 gal gal gal gal gal Micros

17 Foliar Spray at Early Stages Foliar fertilization at early stages increased yield in 15 to 20% of the fields. Many tested Optimum or High. Average yield increase in responsive fields was about 4 bu/acre. Increase across all fields was 0.5 to 1 bu/acre. The most consistent responses were to 3 gal/acre of fertilizer, and a single application usually was enough.

18 Problems Predicting a Response Fields 18 Responsive Fields Soybean Yield (bu/acre) Low soil P and K Stress various (not draught 42 40

19 Foliar Iron in Calcareous Soils Soybean iron chlorosis is common in high-ph, calcareous soils. Several of the 18 sites were calcareous, but we saw no consistent response. Other Iowa research in four fields, two iron chelate products at various rates: no consistent yield increase. Minnesota research: no large yield increase with severe deficiency.

20 Mixing Fluid Fertilizer with Fungicides

21 Treatments at Five Fields Five fields, optimum or higher in P & K Headline fungicide alone 3 gal at V5 to V6 alone at V5-V6 and R2-R3 At R2-R3 + Fungicide 3.3 gal UAN at R2-R3 at R2-R3 alone at R2-R3 + Fungicide

22 Leaf Burn and Green Leaf Area Treatment Burn Green % Control 0 7 Fungicide Only V5-V R2-R V5-V6 & R2-R R2-R3 + Fung UAN R2-R UAN R2-R3 + Fung

23 Disease Control Brown Spot Bacterial Blight Treatment Incid. Sev. Incid. Sev. Control R2-R V5-V R2-R V5-V6 & R2-R R2-R3 + Fung R2-R R2-R3 + Fung

24 Average Yield Results No fungicide Fungicide at R2-R3 Soybean Grain Yield (bu/acre) No fertilizer a V5-V V5-V6 R2-R3 c c c R2-R3 c a UAN R2-R3 d b 40

25 Foliar Fertilization for Soybean Not recommendable across all fields. Tactical use: Target fields to increase the chance of economic return, but criteria to choose fields aren't clear. Cutting fertilization to soil is risky. Can be mixed with some herbicides and fungicides, but conditions that make a response to each product likely seldom are the same.